A processor based system using a processor such as an Intel® Pentium 4 processor may be a personal computer, server computer, workstation, personal desktop assistant (PDA), game system, set top box, or smart mobile phone, among others. Such a system (alternatively termed a platform herein) may include one or more audio input and output devices. These devices may include for example an on-board audio or sound card connected to a bus of the system, such as a PCI Express™ bus; an external device connected to the system by a peripheral bus such as a Universal Serial Bus (USB); or even a remotely connected device over a data network to which audio input data and output data of the system is directed using a network connection, which may be over a network cable or a wireless radio or infrared link. Such a device may provide, for example, the ability to output sounds generated or processed by programs executing on the platform over one or more analog or digital output channels in various formats, such as line level analog audio, SP/DIF digital audio, digital bit streams encoding surround audio such as a Dolby Digital® bitstream, among many others that are known. Similarly, a device may alternatively or also provide audio input capabilities, either in analog or digital format, thus allowing input from, for example, a microphone, line level analog audio source, or digital bit stream with an encoded audio stream in various formats. Such audio input data may then be received, processed, analyzed, and stored by programs of the system to perform various functions.
Such audio capabilities of a processor based system allow in one example, the use of the platform for voice communication over a network using a Voice over Internet Protocol (VOIP). Applications such as Skype and PGPhone address concerns relating to the security and privacy of conversations conducted over VOIP by encrypting voice data before it is transmitted over the Internet or another network. However, data encoding a voice or other communication in an unencrypted format is still generally available on the platform where it is being received or to which it is being sent. This is because either in the initial stage when the voice or message audio is input and in the final stage when it is output, direct memory access by the audio device to a buffer of unencrypted digitized audio data is generally required. This may allow a malicious process on the platform access to the unencrypted audio data. It is possible to circumvent this issue by encrypting audio within the hardware before buffering it, but such solutions would require the installation of new audio hardware. Furthermore, even if audio data is encrypted whenever in digital form, if analog audio is being output from a platform device into, or being input from, the ambient environment, a malicious process may silently use an audio device of the platform in an input mode, such as a microphone, to record the audio data from the ambient environment if such a recording is possible.